Studies are being conducted in animals to determine the in vivo activity of a new class of antimicrobial peptides isolated from the skin of the African frog Xenopus laevis and called magainins. The family of peptides consists of two closely related peptides, each 23 amino acids, that inhibit growth of numerous species of bacteria and fungi in vitro. An animal model of experimental bacterial keratitis induced in adult New Zealand white rabbits were used to determine the in vivo relevance of the antimicrobial activity of magainins. Pseudomonas aeruginosa was primarily considered because it is the most destructive and the most difficult to treat corneal infection in humans. Topical treatment with magainin drops was started immediately after the infection. The control animals were treated with the vehicle or with gentamycin. These studies have shown potential activity of the magainin in the treatment of Pseudomonas corneal ulcers. Although the animals could tolerate the treatment well, magainin drops induced severe chemosis with conjunctival hyperhemia which can aggravate the inflammation related to the infection.